Moon wears dusty cloak
Old data from Apollo missions stir up debate about lunar dust
Beware of lunar dust bunnies. Moon dust may pile up far more quickly than scientists once thought, and the claim is churning up some controversy. Powdery particles resting on the moon’s surface could form a layer up to 1 millimeter thick every 1,000 years, according to a new analysis of old data.
The estimate relies on data dug up from the Apollo missions of the 1960s and 1970s.
“It’s pretty remarkable that we’re still getting results out of 40-year-old data,” says physicist James Gaier of NASA’s Glenn Research Center in Cleveland. Other researchers have used computers to simulate lunar dust, he says, “but we haven’t really had any data.”
Understanding how fast the dust stacks up could help future moon missions deal with the pesky grains.
Apollo 11 gave astronauts and scientists their first taste of moon dust. When the spacecraft descended, the rocket’s engines kicked up dust clouds that made a clear moon landing tricky. When the astronauts ventured outside, dust slicked the ladders, stuck to their suits and tampered with experiments.
The sandlike substance filled in bolt holes, made vacuum seals leak and dulled shiny surfaces intended to reflect sunlight and protect instruments from overheating. Moon dust is finer than flour but sharp, says study coauthor Brian O’Brien of the University of Western Australia in Crawley. “Think of shards of a broken bottle,” he says.
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In 1966, O’Brien invented the first device to measure moon dust. His matchbox-sized gadget housed solar cells and thermometers, and journeyed to the moon with Apollo 11 in 1969.
When sunlight hit the solar cells, they generated an electrical current and beamed voltage data to Earth. The device could detect dust because particles stuck to the cells’ surfaces blocked incoming sunlight, making the voltage drop.
Later Apollo missions carried more dust detectors to the moon, and for six years, the gizmos sent data home every 52 seconds. NASA copied the information onto 7-track tapes but later lost them.
“Back then, nobody gave a darn about dust,” says Lawrence Taylor, a geochemist at the University of Tennessee at Knoxville who worked on the Apollo missions. NASA had so much other data coming in that the dust detector data “sort of fell by the wayside,” he says.
When NASA announced in 2006 that it had misplaced the tapes, O’Brien scrambled to recover the lost data. His personal files held some of the information and he tracked down other researchers to complete the dataset.
In the new analysis, O’Brien and University of Western Australia colleague Monique Hollick wanted to measure moon dust’s natural accumulation rate. So they only used measurements collected hundreds of hours after astronauts left the moon.
To estimate just how much dust had caused the solar cells’ voltage drop, the researchers used results from experiments with fake moon dust. In those experiments, scientists had sprinkled dust on solar cells and measured changes in output. The high rate of dust accumulation that Hollick and O’Brien report November 19 in Space Weather has stirred up wildly different opinions among other scientists.
“It’s just too much dust,” says Taylor. “Nobody will believe it.” He says the estimate is flawed because the simulated dust doesn’t really mimic moon dust. What’s more, other aspects of lunar weather could have perturbed the solar cells, causing similar voltage drops, adds planetary scientist David Williams of the NASA Goddard Space Flight Center in Greenbelt, Md.
Still, at least one other scientist views the dust pileup as relatively small. “This is telling us that if you set something down on the moon, it’s going to stay pretty clean,” Gaier says.
He thinks the new findings could give researchers clues about dust transport over the lunar surface, a topic that’s been controversial. Some scientists think electrostatic forces gently sputter dust over the moon; others believe dust swirls around in sweeping storms. The new results suggest that dust isn’t moving all that much. But, he adds, “The jury is still way out on this.”
More evidence may help resolve the question. NASA’s Lunar Atmosphere and Dust Environment Explorer, or LADEE, is now gliding through the moon’s wispy atmosphere. It began collecting data in November and will measure the amount of moon dust sailing high into the lunar sky.